The invention generally relates to electrostatic motors having low power and small dimensions adapted for use as actuators in microelectronic technology applications for actuating mechanical devices and the like in conditions in which vibrations and shocks take place, such as in the automotive field.
In such applications, there have been proposed electrostatic motor-actuators of the piezoelectric type, in which the conversion of electromechanical energy is based on the reversed piezoelectric effect. These motors have various drawbacks, among which a relatively high cost of manufacture and insufficient reliability, they require quite high supplying voltages and have an insufficiently high efficiency. As a consequence, the use of these piezoelectric motors is not satisfactory usually for the applications mentioned at the beginning, particularly on board motor-vehicles.
Electrostatic linear reciprocating motors are also known, comprising a planar stator having a capacitive structure formed by a metal layer and a layer of dielectric material and a movable member parallel and spaced apart relative to the stator and carrying conductive thin film means defining resiliently deformable projecting feet arranged in contact with the layer of dielectric material of the stator, and means for supplying voltage pulses for applying an electric field between said feet and said metal layer of the stator so as to resiliently deform said feet by electrostatic effect and cause a translation thrust on the movable member along a direction parallel to the stator.
In electrostatic motor-actuators of this type, the use of a huge number of feet (or "petals" or "cilia") enables a vary rapid electrostatic capture effect to be obtained, which insures a very high reliability in operation which in practice is not affected by vibrations, planarity defects of the stator, presence of dust. For this reason, these motors are considered as being adapted for application to microelectronic systems installed on board motor-vehicles.
The peculiar characteristic of the conversion of electromechanical energy at the basis of the operation of these motors lies in that during rolling of the feet of the movable member along the stator an extremely high concentration of energy takes place at the interface between the feet and the layer of dielectric material, with a force equivalent to a pressure in the order of 100-150 kg/cm.sup.2, and as a result of this, the force by which the movable member is displaced linearly relative to the stator reaches values up to 10N. The efficiency of this energy conversion is much greater than that typical of piezoelectric motors, and reaches values in the order of 90%.
However, the electrostatic motors of the above indicated type have some drawbacks, which may be summed up as follows:
relatively high supplying voltage (usually not lower that 200-300 V); PA1 appearance of partial discharges because of the high supplying voltage and the linear dependency between the intensity of the electric field and the polarization of the layer of dielectric material; PA1 formation of concentrated discharges in the layer of dielectric material, which involves the need of using voltage pulses of different polarities; PA1 insufficiently high energy concentration as a result of low permittivity of a dielectric with linear polarization.